Ubuntu 14.04 failed to boot after a failed upgrade to 16.04

I tried to install ubuntu 16.04 beta on my laptop which has ubuntu 14.04 installed 3 days before the official release. So I ran the command

do-release upgrade -d

The download went on well. But during installation, it started showing many errors and suddently the process stopped saying that "too many errors were encountered during the process". I did'nt know what to do. So I restarted the system. But the laptop failed to shutdown but showed a black screen with the led backlight still on. I had to force shutdown the system by pressing the power button. Then when I tried to turn on the system back, It came to black screen showing some errors which I have attached: I have windows 10 also installed on my system and grub seems be working properly but I really want to recover ubuntu which I use more often. Any help would appreciated. Thanks.

First, advice to others who want to install a beta version, besides the classic "backup your data":

• if update-manager -d fails with too many errors and does not rewind what it has done, do not force a restart.
• close update-manager, if necessary, kill the process.
• do an apt-get -f install, followed by apt full-upgrade.
• Repeat with apt update and apt full-upgrade and make sure that the process runs without complaints.

This should let you succeed in 9 of 10 cases. Only then restart into the new kernel.

For your situation:

• Make a bootable installation media (flash drive or DVD) of the latest 16.04.
• Boot into the installer CD.
• Use the repair option with whatever suits you. Try to repair the existing installation, keeping your data - this works surprisingly well.
• After the repair has done its thing, reboot and remove the installer drive.

To clarify what the 'repair' means: When you try to install to an existing Ubuntu system without formatting, the installer detects the existing system and gives you a repair menu in the next step where you can choose to overwrite or repair the existing installation.

You have to choose the install option, it is not mentioned that the repair option pops up later in the process if it is an existing installation.

Enjoy 16.04LTS.